For television and other communication signals which are broadcast from satellite or land-based transmitters, a high quality low-noise receiver is required to detect the received low-level signals and preserve signal quality for faithful reproduction of signal content. Such receivers very typically involve several stages of signal amplification, performed by amplifiers designed using Gallium Arsenide (GaAs)-based transistors and integrated circuits. For each amplifier stage, it is required to provide an appropriate D-C bias to the operating transistors, in the form of prescribed voltages and currents applied to the device terminals. Since the biasing needs of the various stages will, in general, be somewhat different, it has therefore been the usual practice to provide a separate biasing circuit as an integral part of each associated amplifier stage. Thus biasing circuits may represent a significant portion of the electronic content of the receiver.
In today's world-wide environment of proliferating wireless communications, particularly for television which normally is broadcast at high frequencies and at low signal level, these low-noise receivers are manufactured in large quantities, in a very competitive economy which drives continuing reductions in cost and price. In that process, the costs of the amplifier stages themselves are reduced through innovations which reduce piece parts prices as well as the number of parts used, resulting in both material and assembly cost reductions. Increasingly, these ends are accomplished through application of integrated circuit technology for the amplifier components.
In conjunction with the amplifier stage cost improvements, it is highly desirable to provide ways of further reducing the product manufacturing cost for the associated bias circuitry, while maintaining a high level of performance, using the same techniques: parts price reduction, parts count reduction, and monolithic integration of the associated bias circuitry. Since low-noise receivers are by definition operated at very low signal strength, the technical prospect of minimizing the manufacturing costs for correspondingly low power bias circuits is excellent.
There are a number of elements of contribution to be considered in the development of an appropriate bias circuit for these applications. It is significant to note that the key to controlling bias voltages and currents in GaAs devices is that the controlling element of the device is gate terminal voltage, operated at a negative potential with respect to the device source terminal, which is normally at ground potential. Further, low-noise devices offer optimal performance at prescribed drain bias currents, which ideally should be held constant over variations in associated circuit component values and variations in temperature. In terms of manufacture, the bias current should be established automatically, avoiding any need for either labor- or machine-based setting or adjustment in the high-volume, low cost business environment. Further, the biasing system should involve very few parts in order to reduce parts counts and piece-part costs, and also to minimize circuit space which reduces attendant costs of the printed circuit boards, of the metal housings, and of packaging and shipping. The present invention achieves all of these goals.